Polyurethane type elastic fiber, and a process of preparing for the same

ABSTRACT

Disclosed a polyurethane elastic fiber and a method of producing the polyurethane elastic fiber. The method of producing the polyurethane elastic fiber is characterized in that polyol with high molecular weight and diisocyanate with excessive amount are mixed in a condition of a designated shear rate and prepolymerized to produce a prepolymer, the prepolymer is reacted with the chain extender and the chain terminator to produce a polymer, and an additive is added to the polymer and the final polymer is spun. The method of producing the polyurethane elastic fiber according to the present invention improves the stability of the polymer, has an excellent spinnability even in high-speed spinning, and remarkably reduces the generation of wave yarns. The polyurethane elastic fiber of the present invention is excellent in heat resistance, thermosetting efficiency and coherence strength between the monofilaments.

TECHNICAL FIELD

[0001] The present invention relates to a polyurethane elastic fiber anda process of preparing the same. More particularly, the presentinvention relates to a process of preparing a polyurethane elasticfiber, which improves the stability of polymer and has high-speedspinnablity, thereby remarkably reducing the generation of wave yarn.Further, the present invention relates to a polyurethane elastic fiberhaving excellent heat resistance, thermosetting efficiency and coherencebetween monofilaments.

[0002] Polyurethane polymer can be prepared by a one-stagedpolymerization, in which polyol with high, molecular weight of1,600˜2,000 g/mol, diisocyanate with an excessive amount, and chainextender such as diol or diamine compound are simultaneously reacted.Alternatively, polyurethane polymer can be prepared by a two-stagedpolymerization comprising two steps, a first step of that polyol withhigh molecular weight of 1,600˜2,000 g/mol and diisocyanate with theexcessive amount are prepolymerized, thereby preparing a prepolymer, anda second step of that a chain extender and a chain terminator such asdiol or diamine compound are simultaneously reacted with inputted theprepolymer.

[0003] Compared with the one-staged polymerization, the two-stagedpolymerization produces a more regular structure and has a lowerpossibility in a bridged bond, thereby easily regulating the degree ofpolymerization. Most of the polyurethane elastic fibers are now preparedby the two-staged polymerization.

[0004] The first stage of the two-staged polymerization, i.e., theprepolymerization step, is that polyol with high molecular weight, i.e.,diol compound, and diisocyanate with excessive amount are reacted andforms urethane bonds, thereby preparing a prepolymer, in which anisocyanate group is formed on both ends of polyol.

[0005] Generally, the molecular weight of polyol is approximately 1,800g/mol, and the ratio of NCO/OH is about 1.5 to 1.8. The aforementionedprepolymerization is performed at the temperature of approximately 60 to90° C. for 1 to 2 hours in a bulky condition without solvent. As thereaction temperature is higher, the reaction speed is also higher. If asolvent such as Dimethylacetamide (hereinafter, referred to as “DMAc”)or Dimethylformamide (hereinafter, referred to as “DMF”) is used, thereaction temperature is increased by the catalysis of the solvent. Thus,the reaction is finished at the temperature of 30 to 60° C. within 10 to20 minutes.

[0006] The second stage of the two-staged polymerization, i.e., thechain extending step, is that the prepolymer and compound with activehydrogen in a low molecular weight such as ethylene diamine, propylenediamine, 1,4-butadiol are reacted, thereby increasing the degree ofpolymerization. Herein, this compound is used as the chain extender.

[0007] If the prepolymer is reacted with diamine, urea bonds are formed.If the prepolymer is reacted with diol, urethane bonds are formed. Thechain-extending step is faster than the preliminary step and is anexothermic reaction. Therefore, in order to uniformly form the reaction,a polar solvent such as DMAc or DMF is used.

BACKGROUND ART

[0008] Korean Patent Publication No. 196651 discloses a method ofpreparing a polyurethane polymer, in which glycol and diisocyanate(reaction mole ratio: 1.5˜1.64) are mixed in a static mixer at thetemperature of 40˜50° C. and reacted, thereby preparing a first polymerwith non-reacted diisocyanate of 4 mole %. After then, the first polymeris reacted with chain extender comprising ethylene diamine 74 to 80 mol%, 1,2-diaminopropane 19 to 25 mol % and diethyltriamine 0.2 to 0.8 mol%, thereby preparing the polyurethane polymer.

[0009] However, the aforementioned prior art has many problems, asfollows.

[0010] The temperature of 40 to 50° C. is too broad not to uniformly mixglycol and diisocyanate. For example, the reaction of glycol anddiisocyanate is very intensive. Therefore, at the temperature of morethan 45° C., a large amount of glycol and diisocyanate are reactedbefore being uniformly mixed. Thus, it is difficult to uniformly mixglycol and diisocyanate, and a large amount of glycol and diisocyanateare reacted before being uniformly mixed, thereby increasing thepossibility of forming gel caused the reaction.

[0011] In order to maintain the reaction temperature to be less than 42°C., the supply temperature of glycol and diisocyanate must bepredetermined to be less than 42° C. prior to being putted in the staticmixer. However, when the temperature is deviated from 43˜44° C.,impurity such as dimmer is rapidly increased within diisocyanate.Therefore, in order to maintain the reaction temperature to be less than42° C., a heat exchanger must be installed prior to the static mixer oran external jacket is attached to the static mixer, thereby controllingthe temperature. Compared with a method, in which glycol anddiisocyanate are mixed at the same temperature as the storagetemperature (43˜44° C.) of diisocyanate, this method is improper.

[0012] Further, the aforementioned prior art uses diethyltriamine(0.2˜0.8 mol %) among chain extenders, thereby improving the heatresistance and thermosetting efficiency in a subsequent process.However, excessive bridged bonds are introduced within the polymer,thereby decreasing linearity of the polymer and phase transition of thepolymer before spinning. Therefore, it is difficult to stabilize thepolymer, thereby reducing the spinnability. Thus, this prior art cannotincrease the spinning speed more than 650 m/sec.

[0013] Further, Japanese Laid-open Publication No. 4-100919 discloses amethod, in which only ethylene diamine of 0.18 weight % is used as thechain extender, and triamine, tetramine, pentamine, and the like areadded to the polymer prior to the spinning step. However, problems ofthis method are that viscosity of the polymer is very unstable beforespinning, and the spinnability is low. Further, this method improves theheat resistance but decreases the thermosetting efficiency.

[0014] In U.S. Pat. No. 5,362,432, a compound comprising ethylenediamine 83˜92 mol % and 1,2-diaminopropane 8˜17 mol % is used as thechain extender. However, in this method, ethylene diamine with a goodfilling characteristic is comparatively much used, thereby reducing thestability of viscosity of the polymer before spinning. Therefore, it isdifficult to control the process. Further, this method deteriorates thethermosetting of the manufactured elastic fiber.

[0015] Further, in U.S. Pat. No. 5,981,686, a compound comprisingethylene diamine 10˜65 mol % and 1,3-diaminopentane 35˜90 mol % is usedas the chain extender. In this patent, in order to provide a littlebridge to the polymer, amines of three functional group such asdiethyltriamine are selectively used as the chain extender or the chainterminator. However, the aforementioned patent did not apparently statethe amount of the used diethyltriamine. Moreover, U.S. Pat. No.5,000,899 discloses a method, in which a compound comprising ethylenediamine 50˜80 mol % and 2-methylpentamethylene diamine 20˜50 mol % isused as the chain extender.

[0016] Among the chain extenders of U.S. Pat. Nos. 5,981,686 and5,000,899, 2-methylpentamethylene diamine and 1,3-diaminopentane have alonger chain than ethylene diamine and 1,2-diaminopropane,characteristics of an odd chain with 5 carbons, and characteristics ofhaving bulky side chain such as methyl or ethyl. By thesecharacteristics, the aforementioned U.S. Patents prevent an innercrystallization of the polymer or the elastic fiber, i.e.,crystallization due to re-alignment of hard segment and soft segment byphase separation, thereby decreasing the heat resistance. The lower heatresistance reduces the maintenance of physical property in a subsequentprocessing step and removing specific characteristics of the elasticfiber.

DISCLOSURE OF THE INVENTION

[0017] Therefore, the present invention has been made in view of theabove problems, and it is an object of the present invention to providea method of preparing a polyurethane elastic fiber, which improves thestability of viscosity of polymer and has an excellent spinnablity evenin a high-speed spinning, thereby remarkably reducing the generation ofwave yarn. Further, the present invention provides a polyurethaneelastic fiber having excellent heat resistance, thermosetting efficiencyand coherence between monofilaments.

[0018] In accordance with one aspect of the present invention, the aboveand other objects can be accomplished by the provision of a method ofproducing a polyurethane elastic fiber, characterized in that aprepolymer is produced using a continuous polymerizing tube in acylinder pipe comprising a static mixer, a heat raiser, a reactor, and acooler, as follows, and the prepolymer is reacted with a chainextender/a chain terminator to produce a polymer, and an additive isthen added to the polymer.

—As Follows— A Process of Producing the Prepolymer

[0019] (i) mixing polyol with high molecular weight and diisocyanatewith excessive amount within the static mixer with the shear rate ofmore than 20 sec⁻¹ without the inner mixing element,

[0020] (ii) first-reacting polyol with high molecular weight anddiisocyanate with excessive amount within the heat raiser with the shearrate of more than 3 sec⁻¹ without the inner mixing element, and

[0021] (iii) second-reacting the first-reacted compound within thereactor with the shear rate of more than 0.1 sec⁻¹ without the innermixing element, thereby preparing a first prepolymer.

[0022] In accordance with another aspect of the present invention, thereis provided a polyurethane elastic fiber characterized in that coherencestrength between monofilaments is more than 145 mgf.

[0023] In order to provide the shear rate in preparing a prepolymer, thepresent invention employs a continuous polymerizing tube with a mixingelement formed in a Kenics type or a Sulzer type on its inside. Thecontinuous polymerizing tube is shaped in a cylinder pipe. Thecontinuous polymerizing tube comprises a static mixer, a heat raiser, areactor, and a cooler. The static mixer is designed so that the shearrate is more than 20 sec⁻¹ without the inner mixing element. The heatraiser is designed so that the shear rate is more than 3 sec⁻¹ withoutthe inner mixing element. The reactor is designed so that the shear rateis more than 0.1 sec⁻¹ without the inner mixing element.

[0024] First, polyol with high molecular weight and diisocyanate withexcessive amount are mixed within the static mixer with the shear rateof more than 20 sec⁻¹ without the inner mixing element, and reactedwithin the heat raiser with the shear rate of more than 3 sec⁻¹ withoutthe inner mixing element, and reacted within the reactor with the shearrate of more than 0.1 sec⁻¹ without the inner mixing element, therebypreparing a first prepolymer.

[0025] Herein, polytetramethyleneetherglycol with the number averagemolecular weight of 1,700˜3,000 and 4,4′-methylenediphenyldi-isocyanate,which are generally used to produce a polymer for polyurethane elasticfiber, are used. Herein, the mole ratio of diisocyanate per glycol isproperly about 1.5˜1.75. During the process of preparing the prepolymer,three-dimensional bridged bonds are easily generated by theheterogeneous mixture and reaction. Therefore, is it very important toproperly control the shear rate within the static mixer, the heatraiser, and the reactor.

[0026] Without the inner mixing element, the shear rate of the mixturefor the prepolymer within the static mixer is more than 20 sec⁻¹. If theshear rate is less than 20 sec⁻¹, the monomers are not uniformly mixed,thereby forming much gel, and reducing the spinnability and the qualityof the prepolymer.

[0027] Preferably, the mixing temperature of the static mixer iscontrolled to be 43˜44° C. If the mixing temperature is more than 45°C., the reaction is considerably processed prior to the uniform mixing,thereby forming gel of three-dimensional bridged bonds. Components ofgel are accumulated within the static mixer or moved into a next step.Thereby, the replacement cycle of the static mixer is shortened or thequality of the prepolymer is deteriorated.

[0028] Further, the gel influences the final spinning step, therebyreducing the spinnability, generating the wave yarn, and providing a badeffect to the physical property of the produced elastic fiber. If themixing temperature is less than 43° C., since the mixing temperature islower than the storage temperature of diisocyanate, additional equipmentis required.

[0029] Moreover, it is very important to set the shear rate within theheat raiser to be more than 3 sec⁻¹ without the inner mixing element. Ifthe shear rate is less than 3 sec⁻¹, the heterogeneous reaction isincreased and gel is increased within the prepolymer.

[0030] The raised temperature of the heat raiser and the finaltemperature of the raised prepolymer are also important factors. It isdesired to prevent the rapid heat-raising and to set the final raisedtemperature of the heat raiser to be less than 90° C. When the reactiontemperature of the prepolymer is more than 90° C., the side reaction israpidly progressed, thereby increasing the possibility of generating thegel. Further, since the reaction of glycol and diisocyanate is anexothermic reaction, the exothermic reaction must be controlled by wellregulating the heat raising time.

[0031] If the heat raising time is too fast, since it is difficult tocontrol the generated heat during the reaction, the finally raisedtemperature of the prepolymer can be more than 90° C. On the other hand,if the heat raising time is too slow, the equipment of the heat raiseris long with the same supplying amount of the raw material, therebyadditionally installing the heat raiser.

[0032] Further, it is very important to set the shear rate within thereactor to be more than 0.1 sec⁻¹ without the inner mixing element. Ifthe shear rate is less than 0.1 sec⁻¹, the heterogeneous reactiongenerates the formation of the gel. Herein, it is desirable to controlthe reaction temperature of the reactor to be less than 80˜90° C. If thereaction temperature is more than 90° C., the side reaction is rapidlyprogressed, thereby increasing the possibility of generating the gel.

[0033] The prepolymer manufactured by the aforementioned processcomprises gels with a diameter of less than 20 μm. Herein, the number ofthese gels is 600/g. The gels improve the processing property and thequality of the final product. The number of the gels within theprepolymer is measured by a Coulter Counter.

[0034] Next, a chain extender and a chain terminator are added to andreacted with the prepolymer, thereby preparing the polyurethane polymer.More particularly, the prepolymer is solved by a N,N′-Dimethylacetamide(hereinafter, referred to as “DMAc”) solvent, thereby forming a solutionof the prepolymer. This solution is reacted with aN,N′-Dimethylacetamide solution (chain extender) comprising diamine andtriamine, and a N,N′-Dimethylacetamide solution (chain terminator)comprising monoamine. Herein, as diamine used as the chain extender,ethylene diamine or 1,2-diaminopropane may be used. As triamine,diethyltriamine may be used.

[0035] For example of the chain extender solution, a solution comprisingethylene diamine of 60˜75 mol %, 1,2-diaminopropane of 24.9˜39 mol %,and diethyltriamine of less than 0.1 mol % may be used. As monoamineused as the chain terminator, diethylamine may be used. Desirably, thechain extender of 96˜98.5 equivalent % and the chain terminator of4.5˜7.0 equivalent % are used. The chain extender solution and the chainterminator solution may be separately provided, or may be simultaneouslyprovided.

[0036] The prepared polyurethane polymer (hereinafter, referred to as“final polymer”) has a concentration of 36˜38.5 weight % according tothe amount of N,N′-Dimethylacetamide solution for solving theprepolymer, and a number average molecular weight of 30,000˜50,000. Thenumber average molecular weight can be measured by a Gel PermeationChromatography (GPC).

[0037] The polyurethane polymer and an additive are mixed within thestatic mixer without the inner mixing element at the condition of theshear rate of more than 0.13 sec⁻¹, thereby forming a dope just beforespinning. Preferably, the additive comprises triamine group compound.

[0038] More particularly, the additive may be selected from triaminegroup compound, a conventional antioxidant, an anti-yellowing agent, anultraviolet stabilizer, a dyeing improving agent, a dulling agent, or aspinning-enhancing agent. More preferably, as the triamine groupcompound, diethylenetriamine is used.

[0039] In case that diethylenetriamine is not used as the chain extenderbut used as the additive, the bridged bonds are formed in high-speedspinning, thereby improving the heat resistance of the elastic fiber,preventing the precipitation due to re-agglutination of inorganicadditives, and uniformly mixing the additive and the polymer.

[0040] At this time, the uniform mixture of the additive and the finalpolymer is very important. If the mixture of the additive and the finalpolymer is heterogeneous, components of the additive, which are notuniformly dispersed and the mixed, generates wave yarns from the spunelastic fiber, thereby cutting the yarn. Further, the coherence betweenthe filaments is lowered, thereby causing the crack of the filament in asubsequent processing step, and deteriorating the processing propertyand the quality of the final processed fiber.

[0041] In order to uniformly mix the final polymer and the additive, astatic mixer shaped in a cylinder pipe is used. The shear rate withinthe static mixer is more than 0.13 sec⁻¹ without the inner mixingelement.

[0042] The storage temperature of the additive slurry mixed into thefinal polymer is very important. If the storage temperature of theadditive slurry is more than 60° C., factors of the raise and thediscontinuance of the viscosity of the slurry are larger than factors ofthe lowering of the precipitation speed due to micro brown motion,thereby promoting the re-agglutination and the precipitation speed ofthe additive slurry, deteriorating the quality of the additive slurryand promoting the clogging cycle of a filter for the additive.Therefore, the quality and the production of the final polymer areinfluenced.

[0043] Further, if the storage temperature of the additive slurry isless than 40° C., the relative viscosity of the additive slurry againstthe temperature is raised, thereby increasing the generation of thedifference pressure and functioning as an unstable factor of theprocess. And, the micro brown motion is weak, thereby promoting there-agglutination, improving the quality of the additive and shorteningthe clogging cycle of the filter. Therefore, it is preferable tomaintain the storage temperature of the additive slurry to be rangedfrom 40 to 60° C.

[0044] A designated amount of the formed dope is pushed into a spinningtub with the temperature of 180˜280° C. using a gear pump. Thereby, thesolvent included in the dope is evaporated, thus preparing thepolyurethane elastic fiber. This method is referred to as a dry spinningmethod.

[0045] During the dry spinning process, as the final polymer (dope)comprising various additives is changed into a yarn state, the polymeris chemically changed via transamidation or aminolysis. By this chemicalchange, the dope is changed into the yarn state and its molecular weightis increased.

[0046] The number average molecular weight of the elastic fiber, whichis prepared by the present invention, is about 40,000˜70,000. The numberaverage molecular weight of the elastic yarn can be also measured by theGel Permeation Chromatography (GPC). It is proper to set the spinningspeed of the present invention to be 800˜1,200 m/sec.

[0047] The spinning dope produced by the present invention has lowcontent of gel. The additives are uniformly mixed/dispersed within thespinning dope. Therefore, the spinning dope has an excellentspinnability and remarkably reduces the generation of wave yarn. In thepolyurethane elastic fiber produced using the aforementioned spinningdope, a proper amount of triamine is used as the chain extender and theadditive, thereby causing the three-dimensional bridged bonds, andimproving the heat resistance, the thermosetting efficiency, and thecoherence between the monofilaments. According to the heat resistancetest, the strength maintenance rate is more than 54%, and the coherencebetween the monofilaments is more than 145 mgf.

[0048] The number of gel particles of the prepolymer, the molecularweight of the final polymer and the elastic yarn, the stability ofviscosity of the final polymer, the heat resistance, and thethermosetting efficiency of the final polymer are measured, as follows.

Number of Gel Particles of the Prepolymer

[0049] The prepolymer is solved in 1% LiCl DMAc electrolyte by a 0.5%concentration. Then, the number of gel particles of the prepolymer ismeasured by the Coulter Counter (Coulter's product in England)

Stability of Viscosity of Final Product

[0050] The final product is stored in an oven at 50° C. At this time,the viscosity of the final product is measured every two hours for 3days, thereby measuring the rate of climb of viscosity of the finalproduct. Herein, the viscosity of the final product is measured by aBrook Filter RV viscometer using a No. 7 spindle, which has a rotationalspeed of 10 rpm.

Molecular Weight of Final Polymer and Elastic Yarn

[0051] After the sample is solved in 0.05M LiCl DMF solution by aconcentration of 0.05%, the molecular weights of the final polymer andthe elastic yarn are measured by the Gel Permeation Chromatography(GPC). Herein, polyethylene oxide is used as a calibration standardmaterial, and a Waters's product is used as the GPC.

Judgment of Wave Yarn

[0052] The sample with a length of 10 cm is elongated at the speed of500%/30 sec until 500%, and is then left for 1 minute. And, the sampleis also relaxed. If the produced yarn has at least 2 knobs, which arecurved or winds, within a length of 10 cm, this yarn is judged as a waveyarn. The judgment of the wave yarn is represented by the number of thewave yarns among 5,000 cheeses in percentage.

Heat Resistance and Thermosetting Efficiency

[0053] After elongating the sample with the length of 10 cm until 15 cm,the elongated sample is placed in a hot-blast oven at 195° C. for 70seconds. Then, the sample is relaxed and cooled in a standardtemperature and humidity condition for 2 hours and is treated in aboiled water at 100° C. for 30 minutes. The strength before treating,the strength after treating, and the change of the length are measured.The heat resistance is estimated by the strength maintenance rate andthe thermosetting efficiency is estimated by the length change rate ofthe sample. The sample with the high strength maintenance rate has thegood heat resistance, and the sample with the high length change ratehas the excellent thermosetting efficiency. $\begin{matrix}{{{Strength}\quad {maintenance}\quad {rate}\quad (\%)} = {\frac{{Strength}\quad {of}\quad {sample}\quad {after}\quad {treating}}{{Strength}\quad {of}\quad {sample}\quad {before}} \times 100}} \\{{{Length}\quad {change}\quad {rate}\quad (\%)} = \frac{\left( {{{Length}\quad {of}\quad {sample}\quad {after}\quad {treating}} - {{Length}\quad {of}\quad {sample}\quad {before}\quad {treating}}} \right) \times 200}{{Length}\quad {of}\quad {sample}\quad {before}\quad {terating}}}\end{matrix}$

Coherence Between Monofilaments

[0054] One strand of the monofilament is separated by a length of 5 cmfrom the polyurethane elastic yarn comprising plural filaments. One endof the separated monofilament and one ends of other combinedmonofilaments are attached to an Instrung provided with a rod cell ofless than 1 kg so that a contact point between the separatedmonofilament and the non-separated monofilaments is disposed on thecenter of a cage of 5 cm, and then elongated at the speed of 1000%/min,thereby measuring the shear strength of the separated monofilament andthe non-separated monofilaments. A result is obtained by the average ofthe coherences, which are measured during elongation. Each sample aremeasured more than three times.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLE 1

[0055] Polytetramethyleneetherglycol with a 1,800 molecular weight of 1mol and 4,4′-diphenyldiisocyanate of 1.65 mol were putted into thecontinuous polymerizing tube, which is shaped in the cylinder pipe. Thecontinuous polymerizing tube comprises the static mixer with the shearrate of 20 sec⁻¹ without the inner mixing element, the heat raiser withthe shear rate of 3 sec⁻¹ without the inner mixing element, the reactorwith the shear rate of 0.1 sec⁻¹ without the inner mixing element, and10 the cooler. As the static mixer was maintained at 43.5° C., the endof the heat raiser was maintained at 89° C., and the reactor wasmaintained at 88° C. Polytetramethyleneetherglycol and4,4′-diphenyldiisocyanate were reacted for 110 minutes, therebyproducing the prepolymer with isocyanate on both ends. The prepolymerwas cooled to 40° C., and 4,4′-dimethylacetamide was added, therebyproducing a solution including the prepolymer of 45%. Then, as thepolymer solution was cooled to 5° C. and severely mixed, the polymersolution was reacted with N,N′-dimethylacetamide solution of 98.5equivalent %, which is used as the chain extender and comprises ethylenediamine of 59.9 mol %, 1,2-diaminopropane of 40 mol % anddiethylenetriamine of 0.1 mol %, and N,N′-dimethylacetamide solution 6.5equivalent %, which is used as the chain terminator and comprisesdiethylamine, thereby preparing the final polymer. The produced finalpolymer has the number average molecular weight of is 31,000 and theviscosity of 2,200 poise at 40° C., and comprises solid of 38.5%. Thefinal polymer was uniformly mixed with the additive slurry comprising1,3,5-tris(4-t-buthyl-3-hydroxy-2,6-dimethylbenzene)-1,3,5-triazine-2,4,6-(1H,3H,5H)trion antioxidant of 1.2 weight%,1,1,1′,1′-tetramethyl-4,4′-(methylene-di-p-phethylene)disemicarbazidewaste gas stabilizer of 1.0 weight %,N-(4-etoxycarbonylphenyl)-N-methyl-N-phenylformamidine ultravioletstabilizer of 1.5 weight %, titanium oxide of 2 weight %, bluepigment(ultra marine blue) of 0.01 weight %, and diethylenetriamine of0.2 weight %, and being stored at 45° C. within the static mixer withthe shear rate of 0.13 sec⁻¹ without the inner mixing element, therebyproducing the dope just before spinning. The dope is spun using thespinning tub with the temperature distribution between 260˜200° C. bythe dry spinning, thereby producing the polyurethane elastic yarn of 40denier. Table 1 shows the measured results of the number of gelparticles of the prepolymer, the rate of climb of viscosity of the finalproduct, the frequency of generating the wave yarn, the heat resistanceand the thermosetting efficiency of the produced elastic yarn, andcoherence between monofilaments.

EXAMPLE 2

[0056] The same method with that of the example 1 except for using achain extender compound in which a mole ratio of ethylene diamine,1,2-diaminopropane, and diethylenetriamine is 75:24.9:0.1, and using thechain extender of 96.0 equivalent % and the chain terminator of 7.0equivalent % was used to produce the polyurethane elastic yarn. Themeasured results of the number of gel particles of the prepolymer, therate of climb of viscosity of the final product, the frequency ofgenerating the wave yarn, the heat resistance and the thermosettingefficiency of the produced elastic yarn, and coherence betweenmonofilaments were the same as the results of Table 1.

EXAMPLE 3

[0057] The same method with that of the example 1 except for usingdiethylenetriamine of 0.1 weight % as the additive was used to producethe polyurethane elastic yarn. The measured results of the number of gelparticles of the prepolymer, the rate of climb of viscosity of the finalproduct, the frequency of generating the wave yarn, the heat resistanceand the thermosetting efficiency of the produced elastic yarn, andcoherence between monofilaments were the same as the results of Table 1.

EXAMPLE 4

[0058] The same method with that of the example 1 except for usingdiethylenetriamine of 0.3 weight % as the additive was used to producethe polyurethane elastic yarn. The measured results of the number of gelparticles of the prepolymer, the rate of climb of viscosity of the finalproduct, the frequency of generating the wave yarn, the heat resistanceand the thermosetting efficiency of the produced elastic yarn, andcoherence between monofilaments were the same as the results of Table 1.

COMPARATIVE EXAMPLE 1

[0059] The same method with that of the example 1 except that thecontinuous polymerizing tube comprising the static mixer with the shearrate of 19 sec⁻¹, the heat raiser with the shear rate of 2.8 sec⁻¹, thereactor with the shear rate of 0.09 sec⁻¹ without the inner mixingelement, and the additive static mixer with the shear rate of 0.1 sec⁻¹without the inner mixing element were used, and except that thetemperature of the static mixer was 49° C., the temperature of theraised prepolymer was 95° C., the temperature of the reactor was 93° C.,and the storage temperature of the additive slurry was 65° C., was usedto produce the polyurethane elastic yarn. The measured results of thenumber of gel particles of the prepolymer, the rate of climb ofviscosity of the final product, the frequency of generating the waveyarn, the heat resistance and the thermosetting efficiency of theproduced elastic yarn, and coherence between monofilaments were the sameas the results of Table 1.

COMPARATIVE EXAMPLE 2

[0060] The same method with that of the example 1 except for using achain extender comprising ethylene diamine of 70 mol % and2-methylpentamethylene diamine of 30 mol %, and using an additivewithout diethylenetriamine was used to produce the polyurethane elasticyarn. The measured results of the number of gel particles of theprepolymer, the rate of climb of viscosity of the final product, thefrequency of generating the wave yarn, the heat resistance and thethermosetting efficiency of the produced elastic yarn, and coherencebetween monofilaments were the same as the results of Table 1.

COMPARATIVE EXAMPLE 3

[0061] The same continuous polymerizing tube and the additive staticmixer with those of the comparative example 1 was used. And, the samemethod with that of the example 1 except for using ethylene diamine asthe chain extender and adding diethylenetriamine of 0.18 weight % to thesolid of the polymer to produce the dope was used to produce thepolyurethane elastic yarn. The measured results of the number of gelparticles of the prepolymer, the rate of climb of viscosity of the finalproduct, the frequency of generating the wave yarn, the heat resistanceand the thermosetting efficiency of the produced elastic yarn, andcoherence between monofilaments were the same as the results of Table 1.

COMPARATIVE EXAMPLE 4

[0062] The same continuous polymerizing tube and the additive staticmixer with those of the comparative example 1 was used. And, the samemethod with that of the example 1 except for using a chain extendercomprising ethylene diamine of 80 mol %, 1,2-diaminopropane of 19.8 mol%, and diethylenetriamine of 0.2 mol % was used to produce thepolyurethane elastic yarn. The measured results of the number of gelparticles of the prepolymer, the rate of climb of viscosity of the finalproduct, the frequency of generating the wave yarn, the heat resistanceand the thermosetting efficiency of the produced elastic yarn, andcoherence between monofilaments were the same as the results of Table 1.TABLE 1 The Results of Test Gels of Viscosity Wave yarn StrengthThermosetting Coherence prepolymer climb rate generation maintenanceefficiency strength Division (Number) (Poise/Hr) rate (%) rate (%) (%)(mgf) Example 1 500˜600 25 0.1 59 39 145 Example 2 500˜600 29 0.1 62 35150 Example 3 500˜600 27 0.13 54 41 148 Example 4 500˜600 26 0.08 65 33152 Comparative 800˜1,200 31 0.25 54 40 105 Example 1 Comparative800˜1,200 26 0.24 42 42 120 Example 2 Comparative 800˜1,200 48 0.31 6817 124 Example 3 Comparative 800˜1,200 36 0.28 55 39 119 Example 4

INDUSTRIAL APPLICABILITY

[0063] The elastic fiber of the present invention has excellent heatresistance (strength maintenance rate), thermosetting and coherencebetween the monofilaments, thereby being effectively used as a yarn forclothes. The present invention improves the stability of the polymer,has an excellent spinnability even in high-speed spinning, andremarkably reduces the generation of wave yarns.

[0064] Although the preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A method of producing a polyurethane elasticfiber, characterized in that a prepolymer is produced using a continuouspolymerizing tube in a cylinder pipe comprising a static mixer, a heatraiser, a reactor, and a cooler, as follows, and the prepolymer isreacted with a chain extender/a chain terminator to produce a polymer,and an additive is then added to the polymer. —As Follows— [A Process ofProducing the Prepolymer] (i) mixing polyol with high molecular weightand diisocyanate with excessive amount within the static mixer with theshear rate of more than 20 sec⁻¹ without the inner mixing element, (ii)first-reacting polyol with high molecular weight and diisocyanate withexcessive amount within the heat raiser with the shear rate of more than3 sec⁻¹ without the inner mixing element, and (iii) second-reacting thefirst-reacted compound within the reactor with the shear rate of morethan 0.1 sec⁻¹ without the inner mixing element, thereby preparing afirst prepolymer.
 2. The method of producing the polyurethane elasticfiber as set forth in claim 1, wherein the temperature of the staticmixer is 43˜44° C.
 3. The method of producing the polyurethane elasticfiber as set forth in claim 1, wherein the temperature of the heatraiser is less than 90° C.
 4. The method of producing the polyurethaneelastic fiber as set forth in claim 1, wherein the temperature of thereactor is 80˜90° C.
 5. The method of producing the polyurethane elasticfiber as set forth in claim 1, wherein in the chain extending/chainterminating reaction, the chain extender of 96˜98.5 equivalent % and thechain terminator of 4.5˜7.0 equivalent % are added.
 6. The method ofproducing the polyurethane elastic fiber as set forth in claim 1,wherein the polymerized polyurethane polymer and the additive are mixedwithin the static mixer with the shear rate of more than 0.13 sec⁻¹without the inner mixing element.
 7. The method of producing thepolyurethane elastic fiber as set forth in claim 1, wherein the chainextender is a N,N′-dimethylacetamide solution comprising ethylenediamine of 60˜75 mol %, 1,2-diaminopropane of 24.9˜39 mol %, anddiethylenetriamine of 0.1˜1 mol %.
 8. The method of producing thepolyurethane elastic fiber as set forth in claim 1, wherein the additivecomprises a triamine group compound.
 9. The method of producing thepolyurethane elastic fiber as set forth in claim 8, wherein the contentof the triamine group compound is 0.1˜0.3 weight % to solids of thepolymer.
 10. The method of producing the polyurethane elastic fiber asset forth in claim 8, wherein the triamine group compound isdiethylenetriamine.
 11. A polyurethane elastic fiber characterized inthat coherence strength between monofilaments is more than 145 mgf.